The present invention relates to a semiconductor device in which a plurality of semiconductor elements are accommodated in one container wherein the emitter and collector electrodes of each element are connected to terminals drawn from the container. Typically, such devices utilize insulated gate-type bipolar transistors (IGBT).
Previously, in such devices where the semiconductor elements were to be connected in parallel, the collector electrodes located on the bottom of each chip could be connected together simply by affixing the bottom of each chip to an electrically conductive substrate. Connecting the emitter electrodes together required the use of aluminum wires to bond each emitter electrode to a terminal to be drawn from the device. The number of wires needed depended on the intended current carrying capacity of the device, with larger currents requiring a greater number of wires.
Recently there has been demand for IGBT semiconductor devices with larger current carrying capacities. It is important that these devices be compact and have low inductance. Increasing a device's current carrying capacity generally requires that more IGBT elements be integrated in the device. Additionally, in the conventional design heat is dissipated readily through the collector electrode connections but not through the emitter electrode wire interconnections. These factors will increase the size of the device, and necessarily increases the number of aluminum wires to facilitate the emitter electrode interconnections. As a result, the wire inductance will increase and thereby limit the usage of the device in high frequency applications.
An object of the present invention is to provide a semiconductor device which is capable of increased current carrying capacity while reducing the number of semiconductor elements contained therein. This is accomplished by improving the device's heat dissipation characteristics by providing an alternative to the conventional use of bonded wires to make the emitter connections. In the present invention, heat dissipation is not limited to the collector side, but takes place through both the collector and the emitter sides of each IGBT element, even where the device has an increased current carrying capacity. The present invention also provides a device suitable for use in high frequency applications since internal inductance is kept to a minimum due to the lack of wiring.
A semiconductor device according to the present invention has a construction such that a plurality of semiconductor elements are accommodated in one container. Each semiconductor element includes a substrate with an emitter electrode disposed on one side and a collector electrode disposed on the other, opposing side. The emitter electrode of each semiconductor element makes contact with an associated metal contact plate, of which there is at least one metal contact plate for each semiconductor element. The metal contact plates have a thermal expansion coefficient that approximates that of the semiconductor material. Spring means having good thermal conductivity are present between the metal contact plates and the top wall of the container to urge the metal contact plates into firm engagement with the emitter electrodes. The top wall of the container comprises a first terminal, with one face interior to the container and the other face exterior to the container.
Another objective of the present invention is to provide a semiconductor device which also includes a plurality of supporting plates having a coefficient of thermal expansion approximating that of the semiconductor elements. A supporting plate is disposed between the collector electrode of each semiconductor element and the bottom wall of the container.
Another objective of the present invention is to provide a semiconductor device in which the spring means are electrically conductive in addition to being heat conductive, such that an electrical connection is established between the top wall of the container and the metal contact plate.
Another objective of the present invention is to provide a semiconductor device in which each of the metal contact plates is electrically connected to the top wall of the container via an electrically conductive connector plate. Also provided is spring means which include at least one compression spring and an intermediate plate formed of an electrically insulating material exhibiting good heat conductivity disposed between the compression springs and the connector plate. In this structure, heat is conducted through the metal contact plates, the connection plates and the intermediate plates and the compression spring means to the top wall of the container where it is dissipated.
Another object of the present invention is to provide a semiconductor device in which the space in the container, not occupied by the aforementioned elements is filled with a heat-conductive gel material.
Another object of the present invention is to provide a semiconductor device in which the semiconductor elements comprise IGBT's.
Another object of the present invention is to provide a semiconductor device in which the metal contact plates are made of molybdenum (Mo).
Another object of the present invention is to provide a semiconductor device in which the supporting plates are made of molybdenum (Mo).
The effect of the present invention is that heat is conducted from the semiconductor elements via the contact plates and the spring means to the top wall of the container where it is dissipated from the exterior face of the device. Because the heat is dissipated, each semiconductor element will have increased current carrying capacity. Moreover, because electric current is conducted from each semiconductor element through the metal contact plates to the terminal directly or conducted from the metal plates to an intermediate plate to the terminal, there is no longer any need to use bonded aluminum wire connections. Thus the inductance problems caused by the aluminum wires are minimized, making the device suitable for high frequency applications. Heat dissipation can further be improved by filling the remaining space in the container with a heat conductive gel.